So, after some research, I used Calibre to remove DRM from a book that I bought and didn't work right in my Kobo through ADE and it works now!! So probably something to do with firmware and DRM rights with books bought outside the Kobo store? No idea how that works!

Actually from what I understand (I may be wrong about this) but ADE assigns a unique ID to each device you authorise and that is tied to your email address. So if you buy a DRM book you can put that book on as many devices as are authorized and tied to YOUR email address.

From what you said earlier that the book works just fine on your brothers Kobo but not yours would lead me to believe that the book is only authorized for your brothers Kobo & email address. By removing the DRM from the book you remove this restriction.